Research On The Preparation And Properties Of Hydrophobic Electroless Composite Ni-P-Graphite Plating

The Ni-P electroless plating is already widely used in machinery industry because of its excellent corrosion resistance.But due to the plating defects such as pores, pinholes, pitting, etc. the application in bad corrosion environment is restricted.Ni-P electroless composite plating and post-processing can improve the corrosion resistance and extend its application.In so many post-processing of electroless plating, the sealing and hydrophobization surface treatment are effective ways to improve its corrosion resistance.In order to improve the corrosion resistance of Ni-P plating, graphite particles and La³⁺ were added to the Ni-P base plating bath and then the Ni-P-Graphite composite plating was obtained on the 20CrMo surface.Sealing with the TiO₂ Sol and hydrophobization with tetradecanoic acid were selected as the plating post-processing.Metallurgical microscopy, stereomicroscope, microhardness tester, contact angle tester and electrochemical measurement were used to analyze the surface morphology, deposition form, micro-hardness, contact angle and corrosion resistance of electroless Ni-P-Graphite plating.The results indicate that: Graphite particle of 10²0g/L content and La³⁺ were deposited with Ni, P to form Ni-P-La-Graphite composite plating, which increases corrosion potential reduces corrosion current and improves corrosion resistance compared with Ni-P plating; TiO₂ sol-gel method can seal off the plating pores, which can improve corrosion resistance compared with the Ni-P-Graphite plating without sealing; The contact angle on the Ni-P-La-Graphite plating (10²0g/L)surface modified 7⁹ days by tetradecanoic acid was obviously improved, but the contact angle hysteresis was a little big.The contact angle on the Ni-P-La-Graphite plating surface sealing with the TiO₂ sol which was modified by tetradecanoic acid, was up to 147°,and the contact angle hysteresis was 5°; When the contact angle was greater than 120°, the corrosion potential of the Ni-P-Graphite would be increased and the corrosion reduced, then enhance the corrosion resistance significantly and cause passivation.